Amplification of temporally modulated signal beams via two-wave mixing in Bi12SiO20

A theoretical analysis of two-wave mixing in a BSO crystal is developed in the undepleted-pump approximation for a modulated signal beam. It is shown that, for a modulation of high enough frequency, significant ac amplification is possible at three distinct values of pump-beam detuning. A signal beam that is amplitude modulated by a square wave is analyzed by means of the theory, and experimental results are presented in confirmation of the analysis. Finally, it is shown that in the presence of absorption the optimum detunings for dc and ac amplification are different

Excitation of spin waves on a cylindrical semiconductor heterostructure with Rashba spin-orbit interaction

Elementary excitations in a paramagnetic semiconductor quantum well confined to a cylindrical surface are theoretically studied on the basis of coupled spin-charge drift-diffusion equations. The electric-field-mediated eigenmodes are optically excited by an oscillating interference pattern, which induces a current in the outer circuit. For a cylinder with a given radius, sharp resonances are predicted to occur in the steady-state current response, which are due to weakly damped spin remagnetization waves.Comment: 7 pages, 1figur

Single-Beam Holographic Tomography creates Images in Three Dimensions

In digital holography (DH), the interference between light scattered from an object and a reference wave is recorded using a CCD camera. DH has various advantages over analog holography: no film processing is needed, reconstruction is performed using numerical methods, and no further experimental setup is necessary. However, one of the disadvantages of DH is that current CCDs have a resolution of approximately 1,000 lines/mm, which is less than that of photographic film

Nonlinear Self-Organization in Photorefractive Materials

This chapter discusses self-organization and its effects in optics. One of the most exciting and potentially useful areas of current research in optics involves the understanding and exploitation of self-organization in nonlinear optical systems. This self-organization may sometimes lead to the evolution of complex spatial patterns that can be regarded as the nonlinear eigenmodes of the system. Generation of these patterns is characteristically marked by the presence of intensity thresholds. In a nonlinear system with complicated temporal dynamics, it turns out that one cannot retain purity in spatial dimensionality. It is therefore equally important to investigate the dynamics of the transverse spatial variations, which in fact give rise to very interesting patterns due to self-organization. A vast wealth of patterns can be achieved by using a nonlinear optical element with feedback that has the capability of providing field transformation, for example, by spatial filtering. These types of systems are called optical kaleidoscopes simply because of the different self-organized patterns that they can generate

Temporal behavior of two-wave-mixing in photorefractive InP:Fe versus temperature

The temporal response of two-wave-mixing in photorefractive InP:Fe under a dc electric field at different temperatures has been studied. In particular, the temperature dependence of the characteristic time constant has been studied both theoretically and experimentally, showing a strongly decreasing time constant with increasing temperature

Optical Detection of Ultrasound by Two-Wave Mixing in Photorefractive Semiconductor Crystals Under Applied Field

The optical detection of transient surface motion has many practical applications which include, in particular, the vibration monitoring of engineering structures (aircraft, power plants,...) and the detection of ultrasound produced by piezoelectric transducer or by pulse laser excitation. This last application where ultrasound is generated and detected by lasers, presents many advantages over conventional piezoelectric based methods. First, laser-ultrasonics is a remote sensing technique. Consequently it can be used, for example, for inspecting hot materials and products moving on a production line. Second, surfaces of complex shapes can also very easily be probed. For many applications, these advantages compensate the usually lower sensitivity of the laser-based technique compared to piezoelectric transduction

Volume Holographic Recording and Readout for 90-Deg Geometry

When a prerecorded cross-beam hologram is reconstructed (so-called edge-lit readout) with a uniform plane wave and a point source, the resulting exact solutions reveal Bessel-function-type diffracted beam profiles, which are fundamentally modified under weak propagational diffraction. The case of a profiled beam readout with propagational diffraction may be analyzed using a transfer function approach based on 2-D Laplace transforms. In a second series of investigations, dynamic readout from a cross-beam volume hologram recorded with two orthogonal uniform plane waves is considered for various dependences of the refractive index modulation with intensity. Typically, refractive index profiles that are proportional to the intensity (as in the case of Kerr-type media or photorefractives with predominantly photovoltaic effect) and to the derivative of the intensity (as in diffusion-dominated photorefractives) are considered. Two-dimensional nonlinear coupled equations are developed for the two (Bragg) orders for both cases. Closed form solutions are obtained for the first case, indicating only nonlinearly induced self and cross-phase coupling. A simple experiment involving simultaneous recording and readout using photorefractive lithium niobate crystal indicates beam profile distortion, which may be expected in such 90-deg geometries